Anyone in the strength sports world who isn’t training in a cave has surely heard of the keto diet. You know, the diet that lets you eat all the bacon and avocado that you can stomach while shedding fat, maintaining muscle, and still dominating your sport — all you have to do is give up carbs. But will it make you stronger?
The ketogenic diet hasn’t shown any signs of slowing down since bursting onto the mainstream years ago, and it’s still one of the hottest nutrition trends. And while there are many supposed benefits — like making our Navy Seals even deadlier — there’s still some debate on whether or not it can aid strength athletes.
Below, we’ll dive a little deeper into that debate and determine whether athletes can get stronger on a low- or no-carb diet, and if ketosis will help them during their next meet.
What is the Keto Diet, and What is Ketosis?
The ketogenic diet, or keto as it’s more commonly known, is a high-fat diet designed to keep the body in a near-constant state of ketosis, a metabolic state where the body creates ketones from fat to use as energy instead of sugar from carbs (the body’s primary and preferred energy source).
A typical keto diet has 70 percent of your overall calories from fat, 25 percent from protein, and just five percent (about 50 grams) from carbohydrates — though some versions nix carbs altogether.
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Generally, your body will begin producing ketones for fuel a few days after you stop eating carbs — a sure sign is when your breath starts to smell of acetone, a ketosis by-product. Incidentally, it kind of stinks like a mixture of fruit and nail polish remover, in which acetone is a key ingredient. (Note: The only true way to know if you’re in ketosis is to test your ketone levels, which you can do with urine strips, a breathalyzer, or a blood ketone testing kit.)
But don’t worry — acetone is actually a ketone, and while it’s also synthetically made in labs, it’s also naturally produced in the body.
These acetones are a backup energy source for the body. The body prefers carbs, which are digested and then broken down into glucose and converted into energy. Without substantial glucose, the body needs to find a way to continue providing energy to our vital organs (mostly, our brain).
In that sense, there are two forms of ketosis: natural ketosis and nutritional ketosis. Natural ketosis occurs when someone hasn’t eaten carbs in a while — so if you’re on a rigorous hike and forget to pack food, ketosis will kick in as a survival mechanism. Nutritional ketosis, on the other hand, is when ketosis is forced through diet.
Dr. Mike T. Nelson, CSCS, an adjunct professor at the Carrick Institute, whose Ph.D. focused on metabolic flexibility, breaks it down a little more.
“If you look at one of the main fuels the body can burn, carbohydrates and fat are the main two, and a layer down are the sort of ‘subfuels,’ lactate and ketones,” he says. “Historically, ketones have not shown up in the body in enough quantities for the body to use unless you’re starving. But you can get there via the ketogenic diet. When you do that, your body will start producing ketones, which can be used for fuel. Then you’re in a state of ketosis.
Although first suggested as a therapeutic tool by the Mayo Clinic in the 1920s, it wasn’t until the late 20th century that ketosis gained popularity to treat epilepsy and other brain disorders. Some research has shown that more than half of children with epilepsy who go on the diet experience at least 50 percent fewer seizures.
That’s always been its main use: therapeutic. There’s also some shakier evidence that it can help the body fight cancerous tumors and prevent diabetes. (1)
It’s benefits like these that have spurred some corners of the health and fitness industry to try and stay in ketosis in their day-to-day lives. Author and entrepreneur Tim Ferriss has claimed it helped cure him of Lyme disease, and he continues to cycle ketogenic phases to this day. Celebrities like podcast host Joe Rogan, Jersey Shore’s Vinny “the Keto Guido” Guadagnino, and Lebron James have also tried the diet.
It may also help folks to burn more fat while retaining muscle. The promise of a ripped middle mainly caused six-pack aficionados to perk up and the diet to spread like wildfire. From there came communities like Ketogains, where some members can be found swearing up and down, but eliminating carbs increases performance and aesthetics to unprecedented levels.
[Read More: The Best Ab Exercises & Workouts, According to a CPT]
The problem is that while there’s some evidence that ketosis may not be detrimental for some endurance athletes, there’s very, very little clinical evidence as to whether or not it can benefit strength athletes. But we know enough about how the body uses different energy systems to have a pretty good idea.
When Keto Might Work for Strength Athletes
The short answer: when you’re working with low reps. Strength athletes who only have to eke out one to three reps utilize the body’s ATP-CP energy system, which provides small amounts of energy in quick bursts. It’s the first energy source utilized by the body during any exercise, and it’s enough if you’re not working out for extended periods of time. (2)
“Since we don’t have a lot of direct data, you have to ask what energy source are strength athletes using?” says Nelson. “If we look at Olympic lifting and powerlifting, it’s extremely explosive power, the duration of time is concise, so it’s primarily the ATP-CP energy system. So, ketosis in those athletes may be OK because they’re typically doing brief high output with pretty long rest periods.”
He explains that if you’re keeping sets between roughly one and three reps with long rest periods of three to five minutes, this may be long enough to regenerate the ATP levels (a method of intracellular energy transfer) even if you’re in ketosis. However, more volume would require carbohydrates to replenish the body’s energy stores that kick in once ATP-CP has been exhausted.
“So I would say keto is OK — not great — but it’s OK during peaking phases where volume is very low, and you have a very high-intensity effort as opposed to high volume,” says Dr. Mike Israetel, an assistant professor of nutrition, exercise science, and public health at Temple University and co-founder of fitness company Renaissance Periodization. “The higher the total volume of work you perform in training, the more you’re going to rely on glycogen and carbohydrate to potentiate that performance. In strength sports, because the work is typically not as high in duration, people can get away with lower carbs in general.”
When Keto is a Terrible Choice for Strength Athletes
High-rep activity causes energy systems to rely on carbohydrates, so keto isn’t the best choice for strength sports that require lots of volume. That means anyone focusing on functional fitness, CrossFit, strongman, bodybuilding, and any strength sport with high volume should probably stay away from keto.
“The higher the volume of training, the worse keto starts to perform,” Israetel continues, saying that he would even caution against it for sets of more than six reps. “CrossFit is maybe the worst category of sports for which you should try to do keto. It’s an incredibly terrible mismatch.”
When exercising at a high intensity between one and three minutes, the body primarily uses the glycolytic energy system, which — as the name suggests — runs off of glucose, which comes from carbs. If you’re in ketosis, your glycolytic system isn’t running properly, and your performance suffers.
Interestingly enough, people on keto don’t necessarily have low glycogen levels in their muscles. However, if you’re in ketosis and your body thinks it needs to run on ketones, you may not be able to use those stored carbohydrates effectively. Even if your body has all the pieces to run its glycolytic system, it won’t. (At least not well.)
“It’s an access issue, not the amount that’s being stored,” says Nelson. “It’s like a gas tanker truck being pulled over at the side of the road because it’s out of gas. It’s not like there’s no gas in the tanker truck. It’s that there’s no direct line to the engine.“
While the volume is typically a little lower, the same rules apply for strongman; It’s a sport that typically requires 30 to 90 seconds of more or less continuous output, which means it’s an energy system that runs best on carbs.
“As the events turn from the shorter events to the longer events like stone loading, log for reps, deadlift for reps, you would pay for ketosis,” says Israetel. “You’ll have a couple of reps missed on everything. It’s not recommended for performance.”
Endurance runners can sometimes manage well on ketosis because their sport is performed at a relatively low intensity, so an athlete can have some pretty decent performance using ketones as fuel.
It’s also important to note that while it may facilitate fat loss, ketosis is probably lousy for muscle gain. That’s in part because insulin, despite misconceptions that it should be minimized at all costs, is actually highly anabolic.
“In bodybuilding circles where low-carb diets like keto are the most popular, you’ll see an interesting relationship where they’re very popular but only in fat loss stages,” says Israetel. “But in muscle gain phases, very few bodybuilders stay on low carbs.”
Can You “Train Low, Compete High” While on Keto?
Short answer: No. In some corners of the fitness world, runners will train in ketosis to help their bodies better learn to use fat stores for energy, and then, right before a race, they’ll consume a huge serving of carbohydrates. The idea is that the athlete will then be able to efficiently use both forms of fuel that have been adapted to other endurance sports, and while it’s a nice theory, it doesn’t really hold up in practice.
“Research didn’t see much of a performance change, and that’s probably because they gave them a whole ton of carbohydrates while the machinery to use them effectively was impaired,” says Nelson, who notes that the right enzymes to use carbohydrates effectively were not present in high enough amounts. “It probably takes at least a couple of days and maybe a few weeks before those enzymes are back up and running at full steam.” (3)
How Intermittent Fasting May Help Keto Athletes
Two of the hottest fitness trends may actually be able to work in conjunction with each other, at least according to Nelson. There are no studies examining the effect of combining keto and intermittent fasting, but he claims his clients have been able to use better both forms of fuel (carbs and ketones) if they fast for a portion of the day.
“We know that the ability to use fat during rest and low-intensity exercise is highly variable, ranging from 23 to 93 percent,” he says. “So some can use it much more effectively than others. If I think someone’s ability to use fat is impaired, I’ll have them do periods of fasting of up to twenty-four hours or even longer to get that acute change in fat use without messing up their ability to use carbohydrates to the highest degree.” (4)
He has his clients do long, slow, aerobic fasted training once or twice per day to minimize insulin and train their bodies to use fat as much as possible without producing the kind of enzyme changes seen in ketogenic athletes that can reduce the ability to use carbohydrates. “I can give them carbs the very next day, and they can still use them to a high degree,” he continues. “So I’m not screwing up their ability to do strength and power-type activities.”
The Final Word
To recap, there are sometimes that keto might be OK for strength athletes and others when it should be avoided.
- Keto won’t hurt strength athletes who only pump out one to three reps per set, and have long rest periods in between.
- Keto is disadvantageous to endurance athletes because the body relies on glucose from carbohydrates for any prolonged activity.
- Combining intermittent fasting and the keto diet might help people utilize both energy stores (glucose and ketones) efficiently, though no studies prove its efficiency.
“People have been looking for the unique benefits of cutting carbohydrates out for a long time, and outside of some benefits in diseased populations, people with epilepsy, etc., there are just no benefits. It just won’t happen,” says Israetel. “Not surprisingly, there’s no big potentiation effect in anything when you remove something from your diet. So I think that the situation with keto is, can it work in some places where it’s not terrible? Yes. Is it an enhancer? I’ve never seen anything it enhances outside of some disease conditions.”
We love bacon as much as the next person, but maybe don’t forget the home fries.
References
- Poff, A. M., Ari, C., Arnold, P., Seyfried, T. N., & D’Agostino, D. P. (2014). Ketone supplementation decreases tumor cell viability and prolongs the survival of mice with metastatic cancer. International Journal of Cancer, 135(7), 1711–1720. https://doi.org/10.1002/ijc.28809
- Sahlin K. Muscle energetics during explosive activities and potential effects of nutrition and training. Sports Med. 2014;44 Suppl 2(Suppl 2):S167-S173. doi:10.1007/s40279-014-0256-9
- Burke LM, Angus DJ, Cox GR, Cummings NK, Febbraio MA, Gawthorn K, Hawley JA, Minehan M, Martin DT, Hargreaves M. Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling. J Appl Physiol (1985). 2000 Dec;89(6):2413-21. doi: 10.1152/jappl.2000.89.6.2413. PMID: 11090597.
- Goedecke JH, St Clair Gibson A, Grobler L, Collins M, Noakes TD, Lambert EV. Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. Am J Physiol Endocrinol Metab. 2000 Dec;279(6):E1325-34. doi: 10.1152/ajpendo.2000.279.6.E1325. PMID: 11093921.
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